In the field of the art of building of vessels of all types, the reduction of the energy consumed for the propulsion thereof acquires an ever increasing importance in the context of global economic crisis and worsening environmental problems.
Wave making and frictional resistances constitute important parameters that determine fuel consumption during cruising of a vessel. The reduction of frictional resistance and wave making resistance experienced by vessels and the resulting improvement of their sliding through the fluid mass of water that they encounter is therefore the subject of ever lasting efforts. By way of example, the configuration of the stem section of the vessel's hull in the shape of a bulb or in the shape of a ball has been widely used in the past for the reduction of the wave-making resistance and in particular the reduction of the height of the wave generated at the bow of the vessel.
However, the frontal surface of the vessel, i.e. the extensive surface of the bow that is involved in the process of opening a propulsion path through the water surface during propulsion of the vessel is a wide surface with a surface area much more extensive than that covered by the bulb and taking into consideration that the resistance to propulsion is proportional to the square of the speed of the vessel, the horsepower required to confront this resistance and afford cruising of the vessel at the nominal design speed is correspondingly increased.
With a scope of confronting this problem and to reduce the propulsion resistance and accordingly the energy consumed in overcoming wave making resistance that is encountered by the frontal surface of the bow of the vessel, WO-92/22456 of E. E. Petromanolakis has proposed in the past the mounting of a duct at the bow of the vessel, such duct extending at a height above and below the waterline of the vessel and adapted to achieve the reduction of wave generation during propulsion of the vessel as the vessel strikes onto the mass of water body through the abovementioned duct at the bow and not through its entire frontal surface. However, such a wave making energy absorbing duct was not possible to render optimal benefits because the differentiation of flow through the duct in relation to the sea water flow in the surrounding frontal surface of the vessel was rather inadequate. Other attempts of the prior art, such as the French Patent FR-A-1 017 897 had undesirable results, since they not only were not achieving a significant reduction in wave making resistance during the propulsion of the vessel, but they also included mobile portions, which required additional supply of energy from the engine of the vessel and therefore the cost-benefit relationship was unacceptable. Another attempt to manage the sea water flow at the bow of a vessel was disclosed in WO-A-82 03055 (SEE) in which a duct was proposed adapted to lead water from the stem to the stern of the vessel with a scope of its exploitation therein for providing motion to rotatable members, such idea being of a totally distinct philosophy, whilst it is also extremely doubtful whether it can be actually implemented due to frictions, turbulences, etc.
It is therefore a main object of the present invention to efficiently overcome the aforementioned drawbacks and deficiencies of the prior art and to propose structural design parameters of the stem hydrodynamic duct which will allow optimization of the performance thereof. In particular selective combinations are being proposed in the manufacturing parameters of the horizontal wall portion and of the lateral wall portions of the duct, wherein those parameters in the geometry of the wall portions of the duct, which determine the lift coefficient CL and drag coefficient CD are being considered with a scope of obtaining optimization of the ratio CL/CD for both the horizontal and for the lateral wall portions of the duct, as well as of obtaining optimization of the ratio of the lift coefficient CL of the horizontal wall to the lift coefficient CL of the lateral walls of the duct in correspondence with the specific nominal speed of propulsion of the vessel and the geometry of the bow.
On the basis of the parameters being investigated, it becomes possible in all cases of different types of vessels to provide the optimal solution of duct design so as to achieve the best results in the advantageous differentiation of the flow within the duct in relation to the flow in the surroundings outside it and accordingly to achieve a reduced resistance in the propulsion of the vessel with a consequent reduction of fuel consumption.
With a scope of obtaining the above desirably advantageous characteristics, the hydrodynamic duct proposed in the present invention is being arranged with the Center of Low Pressure corresponding to a zero angle of attack onto the horizontal wall portion being located in the region of generation of the first bow wave and with the Centers of Low Pressure of the lateral wall portions in the region of connection thereof with the horizontal wall portion being located in a selected position between the Center of Low Pressure and up to or slightly forwardly the leading edge of the horizontal wall portion.
All these and other objects, characteristics and advantages of the present invention will become apparent in the detailed description herein below.